1. Field of the Invention
The present invention generally relates to a thin film electronic component, and more particularly to a very thin film junction Mott transition field effect transistor (JMTFET), a dynamic random access memory (DRAM) incorporating the same, and a method of forming the JMTFET.
2. Description of the Related Art
Disregarding issues of lithography, the continuation of Moore's Law in scaling of digital circuits reaches a threshold when the dimensions of the MOSFET reaches the physical limits of the device.
Recently, a 60 nm. channel length has been announced as constituting this limit, which may be reduced further by technical advances such as dual gate technology and the like. However, practical considerations such as manufacturing reliability may impose a scaling limit before these physical limits are reached.
The function of the Si-based MOSFET is based on the presence in the channel of the device of a pair of back-to-back p-n junctions, each with an associated depletion layer. The thickness of the depletion layer is a key factor limiting the scaling of the MOSFET to arbitrarily small scales.
In a search for devices which may function as switches compatible with engineering criteria over an extended scaling region below the scales at which the conventional Si-based MOSFET becomes impracticable, the concept of a Mott Transition Field Effect Transistor (MTFET) has been proposed, as set forth in C. Zhou et al., Appl. Phys. Lett., 70.598 (1997) and J. A. Misewich et al., U.S. patent application Ser. No. 08/652,286, filed May 22, 1996, commonly assigned and incorporated herein by reference.
The MTFET is an FET-type device where the channel is made from a material capable of undergoing a Mott metal-insulator transition. Transport in such a channel material essentially experiences a mobility transition as well as a change in carrier number as voltage on the gate changes.
When in its insulating state, the mobility and carrier concentration are low (e.g., mobility less than 0.1 cm/volt sec. and a carrier concentration less than 0.1% per unit cell).
When in the metallic state, there is a high carrier concentration with high mobility, enabling the channel to conduct. The channel function does not depend on a depletion layer or other phenomenon with an extended length scale. Hence, it is predicted to function adequately down to extremely small (e.g., 10 nm.) scales.
Thus, devices based on the Mott metal-insulator transition do not involve depletion layers within the operating channel, and scaling of the MTFET and derivatives, down to much smaller, nanoscopic, dimensions, may be possible.
However, a problem encountered with the use of high dielectric constant materials as gate insulators in both capacitor applications and in MTFET devices is that, when the gate insulator becomes very thin, to achieve switching with 1-2 volt gate signals, the dielectric constant tends to rapidly decrease. This prevents achieving desired turn-on gate voltages.
Thus, working MTFET devices have been realized in the framework of perovskite-based materials. These devices are typically formed by deposition of cuprate layers on to pre-deposited STO gate oxide film, but it is recognized that this process may limit the control of quality at the cuprate-STO interface, which is the most critical part for device performance.